Seam-shifted wake (SSW) is an aerodynamic phenomenon involving baseballs. The term was coined in 2019 by Andrew Smith during his work on the phenomenon with Barton L. Smith (no relation) at Utah State University (USU). Nazmus Sakib and John Garrett also contributed to the early work.
The USU group showed that Major League Baseball (MLB) baseball seams, when in specific locations relative to the direction of the ball, force the Boundary_layer to separate earlier (closer to the front of the ball) than it normally would. If this occurs on one side of the ball and not on the opposite side, a net force is produced. This force can be similar in magnitude to that caused by spin (i.e. the Magnus effect).[1]
In the particle image velocimetry image shown, the seam on the top of the ball is causing separation (wake formation) on the top closer to the front of the ball than normal. The separation on the bottom of the ball is at the normal location.
The resultant movement from this effect had been noted by others before[2] and named the "laminar effect" based on a mistaken notion that smooth portions of the ball caused a laminar boundary layer more prone to separation than a turbulent boundary layer. This was most often discussed with respect to 2-seam fastballs.
Data from MLB on pitch spin and movement, which were not available in 2019, now make it clear that SSW effects are present in most pitches.[3] Seam effects cause two-seam fastballs and changeups to develop addition arm-side movement as well as sink. Four-seam fastballs can gain extra vertical ride as well as glove-side movement. Certain sliders will "sweep" (or move arm-side) due to seam effects.[4][5][6] Some claim benefits from SSW pitches in terms of batter outcomes[7]
Evidence of seam-shifted wake pitches for MLB pitchers can be found by comparing spin-based movement to observed movement on MLB's Spin Leaderboard.[8] These two values being equal indicates no seam-shifted wake, while differences between them (called deviation) are a sign of seam-shifted wake.[3]
Several extensive explanations of how SSW works and what it does to pitches are available.[9][10]
Laminar flow is the concept of fluid dynamics, consisting of how a fluid is going to follow smooth paths on an object. Laminar flow will occur in areas where the ball is flat, in turn exhibiting no force on that area of the ball. The side where the seams are present will experience Turbulence, and cause a force to act on that side of the ball. In turbulence the air is acting trapped by the seam and pushes the seam out of the way as it moves past it, thus creating a force moving the ball in the opposite direction the seam is present. Most of the effect from the turbulence is on the "back of the ball" or the side that is facing the pitcher after released[11]. The laminar flow from the smooth surface of a baseball makes the air move faster across the surface, and is then caught by the seams and in turn creates the turbulence which in turn makes the ball move.
Examples of SSW through the years
Greg Maddux[12] - Greg Maddux was given a ball that had a scuff on one side. He was known for his knee bending 2-seam, however when he threw this ball he angled the scuff on the left side of the ball inturn giving more movement to the right
Shohei Ohtani- Shohei Ohtani's sweeper was the most valuable sweeper in 2023 based off Bwar and runs prevented. It exhibited 3.8 in of movement above the average sweeper in the league.
Paul Skenes[13]- Paul Skenes splinker was the best pitch in the MLB in 2024 based off avg against. It was a sinker with lower than average spin rate and a different axis allowing more downward movement compared to the average sinker.
- ^ Smith, Andrew W; Smith, Barton L (March 2021). "Using baseball seams to alter a pitch direction: The seam shifted wake". Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology. 235 (1): 21–28. doi:10.1177/1754337120961609.
- ^ "Laminar Express: Using Baseball Science to Enhance Two-Seam Fastballs". 21 January 2019.
- ^ a b Barton Smith, Alan M. Nathan and Harry Pavlidis"Not Just About Magnus Anymore". 5 November 2020.
- ^ Eno Sarris"Is there a such a thing as a 'Dodgers Slider'?". The Athletic. 21 October 2021.
- ^ Lindsey Adler "Why the Yankees pitching staff is embracing a new slider and how the 'whirly' is different from a traditional slider". The Athletic. 4 April 2022.
- ^ Eno Sarris"Caught Looking: George Kirby's new slider, building Clarke Schmidt, and the origins of Stuff+ beer". The Athletic. 8 September 2022.
- ^ Eno Sarris "What is 'seam-shifted wake' and which pitchers benefit most from it?". The Athletic. 21 January 2021.
- ^ "Statcast Spin Axis All Pitches". baseballsavant. Retrieved June 22, 2023.
- ^ Barton Smith. "Seam-Shifted Wake Cliff Notes". baseballaero. Retrieved July 14, 2023.
- ^ "AN INTRODUCTION TO SEAM-SHIFTED WAKES AND THEIR EFFECT ON SINKERS". driveline. Retrieved July 14, 2023.
- ^ University, Utah State. "The 'Laminar Express': USU Engineers Dissect the Two-Seam Fastball". engineering.usu.edu. Retrieved 2024-12-03.
- ^ Pitching Ninja (2024-01-09). The SECRET behind Maddux's FILTHIEST Pitch EVER! #mlb. Retrieved 2024-12-03 – via YouTube.
- ^ MLB (2024-06-18). Paul Skenes' SPLINKER is insane 😳. Retrieved 2024-12-03 – via YouTube.